Yellowing Tips/Yellowing Leaves and the Claw

HISTORY:
I am using FFOF soil.
No nutrients have been added.
Plants are appox. 7 weeks old.
Two weeks ago plants were transfered from 1L to 3gal containers.

PROBLEM:
New leaves are coming in w/ a yellow tinge. The tips are the new leaves are yellow.
Mid-leaves are also showing an even yellowing throughout.
All leaves are clawing.

My guess, I am a first time grower, is that i am facing an N deficiency. Any ideas?

I am unable to edit, but my plants are 5 weeks old NOT 7 weeks old.
I also water once a week w/ RO water.

have you been giving it a small dose of nitrogen if not give it a little.

I have not given the plants any nutes thus far.

maybe 1/8-1/4 str veg nutes, don't over do it, the plants still look dark green and lush.

Do you guys think this may be more of a Sulphur, Calcium, or Iron deficiency?

imo i think it looks a little overwatered, i had one do the same thing and die because of it ;( but if not look a lil like a nitrogen def. hope ya fix her!